This invention relates to novel sugar ester derivatives, reagents for measuring activities of lipases or esterases which comprise said sugar ester derivatives as the substrate and methods for measuring activities of lipases or esterases.
Diagnosis of various diseases such as pancreatic diseases is conducted by measuring activities of lipases and esterases which are contained in the humor such as serum, urine and pancreatic juice.
As the methods for measuring activities of lipases, there have been known, for example, methods using an olive oil as the substrate. Such methods include a method which comprises bringing the sample into contact with the olive oil and conducting alkali titration of the isolated fatty acids and a method which comprises measuring, as an index, the change of the temperature in the olive oil emulsion. However, these methods have some defects, for example, in that in these methods, the measurement values change and reproducibility becomes unsatisfactory depending on the difference in the quality of the olive oil as the starting substance and the difference in the way of preparation of emulsions.
The methods for measuring lipase activities which comprise using .alpha.-naphthyl palmitate as the substrate have some problems, for example, that it is impossible to add the substrate in an amount enough to measure the enzyme activities since the substrate is sparingly soluble, that the measurement values vary depending upon the difference in the way of preparing the substrate solution, and that their reproducibility is inferior.
The methods for measuring lipase activities with the use of a synthetic thioester, 2,3-dimercaptopropan-1-ol tributylate (BALB), as the substrate are widely used since their reproducibility and accuracy are relatively better. However, they also have some problems, for example, that the fatty acid ester as the substrate has a short chain and the substrate is hydrolized not only by lipases but also by esterases, and thus the methods lack substrate specificity. Besides, the methods have other defects that since they need a reaction-terminating liquid, they involve complicated procedures and rate assay methods which are considered the most suitable for the measurement of enzyme activities cannot be applied to the method.
In the methods for measuring esterase activities, there are some defects, for example, that it is impossible to add the substrate in an amount enough to measure enzyme activities since the substrate is sparingly soluble, that the measurement values vary in accordance with the way of preparation of the solution of the substrate and that their reproducibility is inferior.
The object of the present invention is to solve the above-mentioned problems and overcome the defects. The primary object is to provide compounds useful as substrates which are free of variation depending on the quality of the starting substances, have a definite structure and have an excellent solubility.
The second and the third objects are to provide reagents for the measurement of lipase or esterase activities and to provide methods for measuring said activities which are excellent in reproducibility and sensitivity and which permit the measurement by rate-assay method by a simple procedure.